The present invention relates to a stereoscopic display apparatus which makes it possible for a person to view different aspects of a display subject by watching while moving round a displayed image, i.e., which makes stereoscopic vision possible.
Stereoscopic display apparatuses adapted to display a stereoscopic image by using a rotating screen have been proposed. In an example of them, data of a two-dimensional image of a three-dimensional substance which would be obtained when the substance were viewed from respective directions around it is created on the basis of three-dimensional image data representing the substance, and the two-dimensional images are projected on a rotating screen one after another. (When creating the two-dimensional image data on the basis of the three-dimensional image data, hidden surface removal processing is conducted to remove data corresponding to invisible portions.) As the direction of the screen is changed by the rotation, the two-dimensional image projected onto the screen is successively changed. When viewing this screen from a certain point, the image displayed on the screen is gradually changed by making the rotation of the screen faster. Since the image display is thus conducted, the image projected onto the screen looks like a three-dimensional image as a result of the after image effect of vision (see, for example, JP-A-2001-103515).
According to the technique described in JP-A-2001-103515, the screen is rotated and a two-dimensional image is projected to obtain a three-dimensional image. If illuminance distribution of the projected two-dimensional image is made uniform at this time, illuminance on the image projected onto the screen becomes lower as compared with the rotation axis side of the screen as a distance from the rotation axis becomes greater, and the illuminance distribution becomes nonuniform. In order to prevent this, a technique of making the illuminance distribution of the projected two-dimensional image nonuniform and thereby making the illuminance distribution of the image projected onto the screen is also proposed (see, for example, JP-A-2002-027504).
In a configuration for picking up images of a display subject from different viewpoints, generating respective slide images, and projecting the slide images obtained by picking up from the pertinent viewpoints each time the rotating screen successively faces to directions of these viewpoints, the rotation speed of the screen is increased to approximately 300 to 600 revolutions per minute to induce after images in the naked eyes and form a pseudo three-dimensional image on the screen. Or in a configuration for continuously picking up images of a display subject with a camera which moves around the display subject, thereby generating a cylindrical film of the picked up images, successively reading the images of the cylindrical film, and forming the images in a spatial position via a mirror rotating in synchronism with reading from the cylindrical film, the rotation speed of the mirror is increased sufficiently and consequently a three-dimensional spatial floating image is generated by after images in the naked eyes. Such techniques are also proposed (see, for example, JP-A-2002-271820).
In the techniques described in JP-A-2001-103515 and JP-A-2002-027504, stereoscopic vision is made possible by using after images. Therefore, it is necessary to display slightly different images nearly at the same time. Accordingly, a sufficiently large number of two-dimensional images become necessary. It requires much labor and takes much time to generate the two-dimensional images. A memory for retaining data of the two-dimensional images also must have a large capacity. Furthermore, since it is necessary to rotate the screen at high speed, it is necessary to project a two-dimensional image corresponding to the direction of the screen onto the screen with high precision. It becomes necessary to maintain synchronization of the screen rotation to timing of projection of a two-dimensional image onto the screen at high precision.
In the techniques described in JP-A-2002-271820 as well, after images in the naked eyes are activated to form an apparent three-dimensional image, by projecting two-dimensional slide images onto the fast rotating screen or forming a two-dimensional image read from the cylindrical film in a peripheral spatial position, with the fast rotating mirror. In the case where the slide images are projected onto the screen, it is necessary to project a pertinent slide image onto the screen when the screen faces to the viewpoint, in the same way as the techniques described in JP-A-2001-103515 and JP-A-2002-027504. Since the screen rotates fast, however, very high precision is needed in timing of projection of the slide image onto the screen.
In the case where three-dimensional image display is conducted by using the two-dimensional images read from the cylindrical film in the techniques described in JP-A-2002-271820, complicated means for successively reading images from the cylindrical film becomes necessary. Furthermore, since the images read from the cylindrical film are subjected to image formation in the space, a clear three-dimensional image can be viewed only in the image formation position, resulting in a very limited viewing position.